title: A comparison of South Asian specific and established BMI thresholds for determining obesity prevalence in pregnancy and predicting pregnancy complications: findings from the Born in Bradford cohort.
abstract: OBJECTIVE
  To describe how maternal obesity prevalence varies by established international and South Asian specific body mass index (BMI) cut-offs in women of Pakistani origin and investigate whether different BMI thresholds can help to identify women at risk of adverse pregnancy and birth outcomes.
  
  
  METHODS
  Prospective bi-ethnic birth cohort study (the Born in Bradford (BiB) cohort).
  
  
  METHODS
  Bradford, a deprived city in the North of the UK.
  
  
  METHODS
  A total of 8478 South Asian and White British pregnant women participated in the BiB cohort study.
  
  
  METHODS
  Maternal obesity prevalence; prevalence of known obesity-related adverse pregnancy outcomes: mode of birth, hypertensive disorders of pregnancy (HDP), gestational diabetes, macrosomia and pre-term births.
  
  
  RESULTS
  Application of South Asian BMI cut-offs increased prevalence of obesity in Pakistani women from 18.8 (95% confidence interval (CI) 17.6-19.9) to 30.9% (95% CI 29.5-32.2). With the exception of pre-term births, there was a positive linear relationship between BMI and prevalence of adverse pregnancy and birth outcomes, across almost the whole BMI distribution. Risk of gestational diabetes and HDP increased more sharply in Pakistani women after a BMI threshold of at least 30 kg m(-2), but there was no evidence of a sharp increase in any risk factors at the new, lower thresholds suggested for use in South Asian women. BMI was a good single predictor of outcomes (area under the receiver operating curve: 0.596-0.685 for different outcomes); prediction was more discriminatory and accurate with BMI as a continuous variable than as a binary variable for any possible cut-off point.
  
  
  CONCLUSIONS
  Applying the new South Asian threshold to pregnant women would markedly increase those who were referred for monitoring and lifestyle advice. However, our results suggest that lowering the BMI threshold in South Asian women would not improve the predictive ability for identifying those who were at risk of adverse pregnancy outcomes.
authors.affiliation: 1] Clinical Trials Research Unit, University of Leeds, Leeds, UK [2] Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK.
authors.forename: M
authors.initials: M
authors.lastname: Bryant
authors.affiliation: Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK.
authors.forename: G
authors.initials: G
authors.lastname: Santorelli
authors.affiliation: MRC Centre for Causal Analyses in Translational Epidemiology, School of Social and Community Medicine, University of Bristol, Bristol, UK.
authors.forename: D A
authors.initials: DA
authors.lastname: Lawlor
authors.affiliation: Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK.
authors.forename: D
authors.initials: D
authors.lastname: Farrar
authors.affiliation: Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK.
authors.forename: D
authors.initials: D
authors.lastname: Tuffnell
authors.affiliation: Edinburgh Ethnicity and Health Research Group, Centre for Population Health Sciences, University of Edinburgh, Edinburgh, UK.
authors.forename: R
authors.initials: R
authors.lastname: Bhopal
authors.affiliation: Bradford Institute for Health Research, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, UK.
authors.forename: J
authors.initials: J
authors.lastname: Wright
mesh_terms: D000328:Adult; D044466:Asian People / Q000706:statistics & numerical data*; D001724:Birth Weight; D015992:Body Mass Index; D003362:Cost-Benefit Analysis; D016640:Diabetes, Gestational / Q000453:epidemiology; D005260:Female; D005320:Fetal Macrosomia / Q000453:epidemiology; D006771:Hospitals, Maternity; D006801:Humans; D007231:Infant, Newborn; D009765:Obesity / Q000453:epidemiology* / Q000208:ethnology; D010154:Pakistan / Q000453:epidemiology; D017410:Practice Guidelines as Topic; D011225:Pre-Eclampsia / Q000453:epidemiology; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology* / Q000208:ethnology; D011256:Pregnancy Outcome / Q000208:ethnology*; D037841:Pregnant People / Q000208:ethnology*; D047928:Premature Birth / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies; D012885:Skinfold Thickness; D006113:United Kingdom / Q000453:epidemiology